FIG. 14 illustrates an example of a condition in which the above-mentioned type image processor is used. In the figure, numeral 1401 denotes a PC(personal computer), 1402 denotes an image processor for enlarging an image that is output from the PC, and 1403 denotes an LCD projector for displaying the output of the image processor 1402.
A video signal is output having as 640×480 pixels from the monitor output line of PC 1401. The image processor 1402 for performing resolution conversion is connected between the PC 1401 and the LCD projector 1403 so as to display the video signal on the LCD projector 1403 which has a resolution of 1280×960 pixels.
Thereby, a low-resolution image output from PC 1401 is converted to a high-resolution image, and even when an image of a PC is subjected to an enlarged projection display on a screen by the LCD projector 1403, the projected image is prevented from being roughly displayed.
Various methods have been proposed for resolution conversion processing which enlarge a low-resolution image by interpolating. The most common method is a linear interpolation for linearly interpolating an intensity of new pixels from peripheral original pixels.
FIG. 4 is a diagram showing an interpolation position of pixels according to the conventional linear interpolation method.
In FIG. 4, numeral 401 denotes an original pixel with intensity G, 402 denotes an original pixel with intensity H, 403 denotes an original pixel with intensity 1 and 404 is an original pixel with intensity J. The interval between these original pixels of low-resolution image, that is, the interval between adjacent pixels in each of the horizontal or vertical directions is “1”. Numeral 405 denotes a new pixel with intensity K which is obtained by conventional linear interpolation. “m” presents the distance from the original pixel 401 to the new pixel 405 in the vertical direction, “n” presents the distance from the original pixel 401 to the new pixel 405 in the horizontal direction, and these distances “m” and “n” are assumed to be 0≦m<1 and 0≦n<1.
The intensity K of new pixel 405 will be calculated by the following equation.K=(1−m)((1−n)G+nH)+m((1−n)1+nJ) 
According to the conventional linear interpolation, it performs interpolation by linear interpolation and the required operation times for calculating the new pixel is six times of multiplication and five times of adding and subtraction.
In the conventional linear interpolation, there is a problem in that an image is smoothed by averaging processing with peripheral original pixels, thereby resulting in blurred images with the edge parts thereof lacking in sharpness.
There is an image processor disclosed in the Japanese Published Patent Application No.7-93531 which can solve the problems that the edge parts of an image is blurred by averaging processing. The image processor is one which performs linear interpolation arithmetic as well as performs smoothing after adding arithmetic processing for creating edges in accordance with the condition of peripheral images. Thereby, the edge parts are cleared, resulting in high-quality images.
However, the image processor disclosed in Japanese Published Patent Application 7-93531 has a problem in that the entire processing time is increased as well as the device becomes costly when constructed in hardware, because it requires an edge making arithmetic processing in addition to the linear interpolation.
Further, when a low-resolution image is interpolated and converted to a high-resolution image, in particular, to an image having twice the number of pixels in each of the vertical and horizontal directions, the amount of arithmetic processing can be reduced by devising the pixel arrangement. The arrangement in this case will be described with referring to FIG. 6.
FIG. 6 is a diagram showing a pixel arrangement when performing resolution conversion to twice the number of pixels in each of the vertical and horizontal directions by a conventional image processing method.
In FIG. 6, “∘” designates an original pixel of low-resolution image, “□” designates a new pixel of high-resolution image. The pixel arrangement in FIG. 6 omits arithmetic processing for calculating the intensity of a new pixel 604 by matching the position of an original pixel 601 with the position of new pixel 604, and matching also for their intensity. In addition, a new pixel 606 is calculated based upon the original pixel 601 and the original pixel 602, and a new pixel 610 is calculated based upon new pixels 606, 607, 608 and 609.
According to the pixel arrangement in FIG. 6, though the intensity of new pixel 604 which corresponds to the original pixel 601 includes no error, the intensity value of new pixel 606 which is calculated based upon the original pixels 601 and 602 may include an error. Further, the intensity value of new pixel 610 which is calculated based upon the new pixel 606 may include a greater error. Thus, there arises an interpolation result in which the appearance probability of error varies depending on the intensity of the new pixel.
As mentioned above, the conventional image processing method for converting a low-resolution image to a high-resolution image performs averaging of the intensity of original pixels at a periphery of a new pixel, thereby resulting in a problem that an interpolated image is smoothed and results in blurred images in which edge parts thereof lose sharpness.
Further, the image processor disclosed in Japanese Published Patent Application 7-93531 has a problem in that the entire processing time becomes longer due to an edge making arithmetic processing and a problem in that it becomes costly when it is produced in hardware.
Further, in a case where a pixel arrangement is devised so as to decrease the amount of arithmetic processing, there may be a case in which the appearance probability of an error of pixel data varies depending on pixels.
The present invention is made to solve the above-mentioned problems and has for its object to provide an image processor, an image processing method and an image processing program recording medium which can obtain a high-quality image with sharpness which requires a decreased amount of interpolation arithmetic so as to improve an image resolution, decrease processing time, and provide a small scaled hardware, and further, which can make uniform the appearance probability of error of pixel data in a case where a pixel arrangement is performed so as to minimize the amount of arithmetic processing.